Base for electric discharge lamp



July 18, 1961 H. PlETzscH ETAL 2,993,191

BASE FOR ELECTRIC DISCHARGE LAMP Filed 'March 25, 1957 Fi .7 1a 19 23 g so 2s 31 Fig-3 23 @lY vih 1i 17 E W'm-' i' INVENTORS HERBERT PiEuscH oTToKAR SORGE ATTORNEY nited States Patent 2,993,191 BASE FOR ELECTRIC DISCHARGE LAMP Herbert Pietzsch, Berlin-Haselhorst, and Ottokar Sorge,

Berlin-Frohnau, Germany, assignors to Patent-Treuhand-Gesellschaft fr elektrische Gluhlampen m.b.H., Munich, Germany Filed Mar. 2S, 1957, Ser. No. 648,135 y Claims priority, application Germany Mar. 28, yr1956 6 Claims. (Cl. 339-145) This invention relates to a base for electric discharge lamps and relates more particularly to a transparent or translucent base for lamps having tubular glass bulbs, .the ends of which are closed by what is termed a lamp stem including a glass tubular member having a ared end which is fused to the end wall of the tubular lamp bulb. Lead wires are sealed through the stem and are electrically connected to the contact pins of a base when the base is secured to an end of a bulb by a suitable cement.

In common practice the bases used for discharge lamps vary in form, composition and structure and are of opaque material out of harmony with the light transmitting area of the bulb. The advantage of being `able to provide a light transmitting base will be readily understood. Certain diiculties arise, however, in the use of a transparent material which involves not only the provision of a satisfactory material but in the means for securing the base to the bulb which brings in the need for a transparent cement. Cements for this purpose lhave not only been found impractical in not being suitable to meet temperature conditions, but, in the increase in the thickness of the material through which the light must pass.

' It has been found, however, that a transparent or translucent base, meeting the requirements essential to manufacture of a practical and commercial article, may be had by the use of an artificial resin which, yas will be explained, surmounts the diiiiculties heretofore encountered.

The resin selected has a modulus of elasticity of as low as about 5,000 kg./cm.2 and as high as about 19,000 kg./cm.2 with a breaking dilation of more than 50% and -as high as about 230% and which has an initial softening temperature of as low as about 150 C. and as high as about 210 C. A modulus of elasticity which is greater than 5,000 kg./cm.2 or a breaking dilation which is greater than 50% as disclosed in the present invention is required because otherwise it is not possible to pull the base over the tube end at room temperature and without heating. Also, during operation of the lamp in a closed envelope there is a temperature of about 130 C. in the surroundings of the base. In order to prevent with certainty any deformation of the base by heat in use, the base material must have a suciently high softening tern` perature or a sufficient constancy of form or shape at the temperatures occurring in operation. These characteristics are found in certain dicarboxylic acid polyamides land obtainable on the market under the trade name Ultramid S. The breaking dilation is a percentage of increase of length to original length at moment of breakage, at room temperature and may be expressed by the formula -X l=percent breaking dilation wherein L means the increase of length in mm. on drawing of a test piece at the instant of breaking, and L0 means the original length in mm. of the test piece.

' When -a lamp base in accordance with the present invention is formed of the above material, it has been found that, not only may the base be readily formed or molded about the bulb neck, but the material of the base, after being heated until it softens, will after cooling adhere to ICC the glass bulb, making the use of a cement unnecessary. It was also found that the union between the glass bulb and the base was so effective as to meet prescribed torsion tests.

In practice it Was ascertained that the high heat spread coeiicient of expansion, of the order of magnitude of the base material selected, also results in a speedy adherence of the base to the bulb if the base is applied to the bulb end when the bulb is heated above the softening point of the base material, and if the base is cooled down quickly below the softening point of the base material. Furthermore, by reason of its higher coeiiicient of expansion, the base contracts faster and becomes firmly attached Ito the bulb, and because of the high breaking dilation of the base material, no cracking or distortion occurs due to the shrinkage of the base after cooling.

As stated, a base of the material set forth is elastic to such degree that in certain cases the use of heat may be dispensed with and the base may ybe attached to the bulb by the application of pressure. In this case the base wall or rim may be provided with an annular rib extending inwardly. The base may then be applied to the bulb neck and the rib forced over the bead and groove which is formed on the bulb as a result of the sealing operation. The rib is moved into the groove between this bead and the bulb proper.l This operation may be performed when the base is at a temperature below the softening point as, for example, at room temperature. It has been found that the base when so applied is securely attached to the bulb. If necessary to prevent rotary movement of base relative to the bulb, the base may be formed with ribs to be disposed into grooves provided in the bulb neck.

The material employed for the base may be clear, translucent or diffusing. Its transparency at a thickness of 1 mm. amounts to at least 30% which is satisfactory. It may be desirable to obtain light radiation emitted through the glass lamp wall and through the base of not only the same intensity but also of the same color. The base material may, therefore, be the same color or luminescent material may be added.

The present base composed of the material above set forth is of particular advantage when the lamps are put to use in tropical countries, since the base material absorbs very little moisture. If the base is immersed in water for 24 hours, its weight is increased by less than #1% and its weight after complete saturation about 3% to 4% or less than 5%.

The present invention is primarily directed to the provision of a lamp base of a light transmitting material.

It is also an object of the invention to provide a base of transparent material for use with an electrical discharge lamp.

Another object of the invention -is to provide a lamp base of a transparent material capable of deformation to engage and secure the base to the bulb end.

Another object of the invention is to provide a base composed of a material capable of being reformed When `subjected to heat to tightly embrace a bulb surface to secure the base thereto.

Another object of the invention is to provide a base composed of a material which when subjected to heat may be reformed to make firm contact with a bulb neck and which contacting base surface adheres to the surface of the bulb.

Another object of the invention is to provide a light transmitting base composed of a material having an annular portion deformable to make rm contact with the surface of a lamp bulb and which will cement the base to the bulb surface to secure the base in xed relation to the bulb.

The invention will be more clearly understood by reference to the following description together with the accompanying drawing, in which; V n

FIGURE@ is an elevationof an end portion of a tubular lamp bulb with an annular trough and and with diametric notches in accordance with the present invention; p n Y FIGURE 2 is a bottom view of the bulb shown in FIG. l;

FIGURE 3 is a cross-section of a base to beV attached to the bulb of FIG. l; Y p l FIGURE 4 is a plan of the base shown in FIG. 3;

FIGURE 5 is a cross-sectional view of a 'modified form of base;

FIGURE 6 is a plan of the base shown in FIG. 5; and

FIGURE 7 is a cross-sectional view of a base of the` type of FIG. 3 assembled on a bulb of the showing of FIG. l.

In the selected embodiment of theV invention, as illus trated in the drawing, an end portion of a tubular bulb 11 is shown in FIG. 7 with a base member or cap 12 secured thereto, the bulb being shown separately in FIG. 1Y and the cap separately in FIG.' 3. The end of the tubular bulb 11 is closed by what is termed a lampfstem or lamp-` seal, which includes a flare tube I3 including a tubular and flared portion surrounding an exhaust tube. When the ared portion of the stem is sealed tothe tubular buld end, a thickened portion in the form of an annular rim or bead 14 is formed of less diameter than the outside diameter of the tube and spaced therefrom by an annular recess `or trough 15.

In accordance with the present invention theV base member l2 is in the form of a cap having a bottom Wall or disk 16 surrounded by a side Wall 17. The central portion of the bottom wall is thickened at 18' to receive and secure contact pins 19 which extend from the outer surface of the base vand are tubular to receive lead wires (not shown) of the lamp. Centrally located on the inner surface of the thickened wall or land 18 is a depression 21-to accommodate the end of anexhaust tubewhen the cap is secured to the bulb. This depression or reduced thickness of the land 13 permits slight distortion of the base of about l to 2 mm. in the event of impact as in the event that the lamp is mishandled or subjected to a fall. e

When the base or cap is positioned With the4 annular wall ,17 adjacent to the trough of a' bulbV end which has been heated to about 300 to 350 C., preferably to about 330 C., the base material melts and occupies the trough or channel and by reason of the-character of the material of which the base is composed, adheres to the surface of the glass bulb;

The base is quickly cooled in about ten to fifteen seconds to below its softening temperature, which is less than 210 C., causing the base material to shrink or contact about the bulb neck. This is due to the higher coecient of expansion comparedrto that of the glass by reason of the particular material of which the base is composed and employed in accordance with the present invention to provide a lampY Lbase. The coe'cient of longitudinal extension of the material used vamounts to 14 to 16.10-5c7 C. but that of glass amounts to only 0.7 to 0.9-105-5" C. f Y v A'base of the type shown in FIGS: 3, 4 and 7 and provided with transverse or radial ribs may -in some cases be applied to the bulb neck without heating-of the'bulb neck. It has'been foundin practice that `owing to the high modulus of elasticity (19,000 kg./cm.2 ofthe material employed for the base, the base kmay be pressed against .thefbulb end lto cause the annular lrib-or reinforcement 22 to snap over the bead or rim 14 and into trough or channel 15 of the bulb to thus secure the base against relative endwiseV Amovement Y with Y respect. to the `bulb ranclto position the radial ribs 23 in the notches 24to prevent rotary movement of the base relative Yto the bulb.

As shown in FIGS. 6 and 7, the base may be in the form of a disk Z5 which requires less material than when in the form of a cap or cup. The outside diameter of the disk-base 25 may be about the same as that of the' rim or bead 14 of the bulb. yThe base ZSis pressed against the bulb end and heated by ycontact with thehot bulb, or otherwise, above the melting point of the base material and quicklykcooled. Where contact is-` made between the surface 26 and bulbV the material ofthe base adheres rmly to the glass. Since, in the bulb sealing operation variations may occur in the diameter or tapering of the are tube of the stem, the contact surface 26 of the base may be conical, receding from the center to provide surface 27 for eiective contact withY the flare tube of the stem. This disk-base may also be provided with radial ribs 28 to engage notches in the rim of the bulb to prevent relative rotary 'movement and has a cavity 29 to accommodate the'end of an exhaust tube.

FIGURES 5 and 6 show what may be termed a conical reinforced base which is of advantage from a production standpoint, since it may be readily die cast. Whenv applied, it is pressed against the heated bulb neck and secured by virtue of heat from the bulb, or otherwise, softening the material of the base and effecting a contraction radially inwardly to thereby form an arcuate rib seating in trough 15 and adhering to the "glass` of the bulb thereat. As shown, this base is provided with an end wall or disk 33 and an annular reinforcement 3 1 and has an inclined wall 32' and a depression 30 tore'ceive an end of an exhaust tube and may be provided with radial ribs 23. i

As will be evident from the foregoing, the present invention not only providesi a more desirable type of base from the light-transmitting standpoint, but makes use'of a material capable of being deformed or molded into xed relation with a bulb neck and provides the'added important feature of beingY rendered adherent t'o cement the parts together. By reason of the properties'and workability of the material employed, it not only is found desirablev for use to provide'a base but may be employed to provide a transparent or translucentso'cket.

Although a preferred embodiment of the.V invention is shown and described herein, it will be'understood that modifications may be made therein without departing from the spirit and scope of the invention, as setV forth in the appended claims.

What is claimed iszV r l. In combination, a tubular discharge lamp bulb hav# ing an end closed by a stem seal and providing thereat an annular rim and an annular trough between the body of said bulb and said rim, said rim having two diametrically opposed notches, and a base dimensioned for making pins arersealed.

direct physical contact with at least Va part ofthe exterior of said bulb end, said' basen comprising Vlight-passing material and being in the form of a cap comprising a disk and an annular wall, said disk having twoV radial ribs diametrically opposed for engaging in `said notches to retain the base against rotary movement relative to said bulb,v said disk having base pins therein and projecting therefrom in a direction away from the'bulbV body, and said annular wall having an inturned ribV adjacent to the annular edge of said wall remote fromthe disk, saidrib engaging said trough and fastening the base to the' bulb.VV

2. A combination in accordance with claiml wherein saidV disk is providedV with a reinforcementxtending coaxially inwardly therefrom and into which said base 3. A combination in accordance with claim 2, wherein said reinforcement provides a central depression toward the bulb andofless diametric dimension than the diametric spacingr'between Ysaid base pins to receive an end of an exhaust tube.v l v er.. Y f

4. A combination in accordancewith claimjl, wherein said capv is frusto-conical with its smaller endV constituting said disk and its annular wall being inclined outwardly therefrom at the periphery thereof with the maximum diameter of the inclined wall remote from said disk and providing said inwardly directed annular rib thereat around said end of the bulb in said trough thereof.

5. A combination in accordance with claim 4, wherein a reinforcement is provided extending in the same direction as the axis of and within said cap toward the bulb, and said base pins being sealed in said reinforcement.

6. A combination in accordance with claim 5, wherein said reinforcement provides a central depression in its end toward the bulb to receive an end of an exhaust tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,009,220 Bols July 23, 1935 2,094,648 Fritze et al Oct. 5, 1937 2,134,472 Criger et a1. Oct. 25, 1938 White et a1 Apr. 18, 1939 Carothers Feb. 20, 1940 Origer et al Jan. 6, 1942 Gordon Feb. 2, 1943 Harrison Jan. 11, 1944 Baxter Sept. 25, 1945 Thomas Jan. 8, 1946 Yoder Dec. 26, 1950 Stevensv Mar. 25, 1952 Crawford July 7, 1953 Marz Ian. 31, 1956 High et al Nov. 11, 1958 OTHER REFERENCES 15 British Plastics-Nylon the ,Latest Synthetic Material- April 1940, pp. 408-409.

Modern Plastics-The News About the Nylons, Vol. 32, No. 12, August 1955. 

